The
buddy of a racer saw my carburetor shop work shirt while we were watching
cars launch on test day. He asked, "Hey, my buddy just got a new, bigger
Holley and we can't get it jetted right. It's slower now than it was with
the smaller carb. What's the deal?" As it turned out, just the reverse
was true. He bought a Holley "HP 950" and took off a Holley "850."
It's understandable why he made the mistake of thinking he'd gotten a "bigger carb." After all, 950 is more than 850 right? Wrong! In this case, Holley decided to rate their new line of "HP" carbs like their competition does, with inflated CFM figures. They had to. Otherwise no one would buy them because they are more expensive. An HP 950 Holley is a 750 main body with an 850 base. That makes it an 800. You can do the math. The "950," in this case, refers to the CFM potential, not the size of the venturi and throttle blade diameter.
Do
not be misled or confused by the difference between CFM and size--all custom
carb companies sell their carbs by the CFM potential instead of the size because
they know that it's harder to get a large sized carb to feel responsive at
low rpm with wide throttle angles. You could say that the smaller is easier
and bigger is stronger. The smaller sized carbs don't need as much professional
help to make them work their best, but the bigger sized carbs will make more
horsepower at top end when they are working at their best.
You can't expect to bolt on a carb fresh out of the box, or any race part for that matter, and it be just right. It will need on-the-car tuning to correctly work your combination. The fact is, the only Holley that's bigger than the 850 is the Dominator (the HP 1,000 is an 850 with air-horn treatment.) I explained the above to my new racer buddy and he got a refund and bought a 1050 Dominator. After I "tuned it on the car," it ran better and stronger than ever. I even made it more streetable.
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